The invention relates to bumper bars for a motor vehicle, whether these are front bumpers or rear bumpers.
It is known that the behavior of vehicle bumpers in the case of an impact can be studied by means of various tests more or less standardized, in particular, by the regulations in force in Europe and in the United States of America. There are essentially four such tests.
First of all, there is the test known as the xe2x80x9cparking impactxe2x80x9d test. It takes place at four kilometers/hour in Europe and at eight kilometers/hour in the United States. In the course of this test, only the absorber of the bumper is supposed to be deformed, without prejudice to the bumper bar itself.
Another of these tests is that known as the xe2x80x9cpedestrian impactxe2x80x9d test. It is intended to reduce as far as possible the injuries suffered by a pedestrian when struck by a vehicle at low speed.
Another of these tests is that known as the xe2x80x9curban impactxe2x80x9d test. In Europe, it is also called the xe2x80x9cDANNERxe2x80x9d impact or xe2x80x9crepairability impactxe2x80x9d. In the course of this test, the vehicle strikes a rigid wall at a speed of sixteen kilometers/hour, the wall extending over 40% of the width of the vehicle. In the course of this impact, the bumper should be damaged preferentially so as to protect the chassis of the vehicle, especially the longitudinal members.
Finally, the fourth test is that known as the xe2x80x9chigh-speed compatibility impactxe2x80x9d test. In the course of this test, the vehicle strikes a barrier covering 40% of the width of the vehicle at sixty kilometers/hour. This standardized barrier comprises a deformable aluminum buffer with a honeycomb structure rated at 50 psi (compression load), this buffer being followed by a honeycomb wall likewise rated at 50 psi. During this impact, the bumper bar, which is mounted on the longitudinal members of the vehicle, should be capable of deforming the barrier in a uniform manner without tearing the latter. In particular, tearing of the barrier by the longitudinal member of the vehicle should be avoided. The bar must not break and should deform the barrier until it is bearing on the engine. It is a matter of ensuring that the bar deforms the buffer, starts to deform the barrier and, without the bar breaking and in the course of the crumpling of the barrier, the longitudinal member itself begins to crumple. Once the bar is bearing on the engine, it is considered to have played its part. To avoid piercing the barrier with the longitudinal member, it is important to distribute the force over the entire bearing surface of the bar. Another thing that should be avoided is the bar wrapping itself around the barrier. To pass this test, the bar must be rigid so as to distribute the forces over the barrier.
In this context, bumper bars made of steel or aluminum have been proposed. However, bars made of steel are found to be very heavy, while bars made of aluminum are relatively expensive.
Bars made of a composite material based on plastic, possibly reinforced with glass fibers, have likewise been proposed. However, these bars generally do not have an appropriate impact resistance. In fact, they break into several pieces or are not rigid enough to deform the barrier in the case of a high-speed impact.
The patent EP-0 625 104 discloses a bumper bar with an H-shaped section provided with a network of oblique transverse ribs extending between the front and rear walls of the bar along the entire length of the latter. This bar is designed to pass the xe2x80x9cparking impactxe2x80x9d tests required on the American market.
It is an object of the invention to provide a bumper bar which behaves well during an urban impact and to an acceptable standard during a high-speed impact as well as during a xe2x80x9cparkingxe2x80x9d-type impact or a collision with a pedestrian, but is not prohibitively heavy or prohibitively expensive to manufacture.
To achieve this object, the invention provides a bumper bar for a vehicle, comprising front and rear walls and an intermediate web extending from the front wall to the rear wall so as to form with the latter an xe2x80x9cHxe2x80x9d-shaped section, the web having an undulating shape in cross section.
In experiments, the applicant has surprisingly found that the shape of this web improved very considerably the behavior of the bar during an impact, in particular during an urban impact. In fact, the undulating shape allows the web to concertina during a frontal impact, such that the bar poses moderate resistance to crumpling in the sections where the web is present. In contrast to a conventional xe2x80x9cHxe2x80x9d-section bar with a strictly flat web, in which the web plays a dominant role in guiding the crumpling of the bar, in the bar according to the invention the undulating web plays a minor role in guiding the crumpling, the crumpling being determined in large measure by other parts of the bar. However, the behavior of the bar during the impact can be significantly influenced by modifying the amplitude of the undulation and the dimensions of the web, in particular its thickness.
Of course, during any of the impacts mentioned above, the overall structure of the bar influences its behavior. Thus, even if certain parts of the bar have a decisive effect on this behavior, it remains difficult to identify precisely the exact role played by any particular part of the bar. This is the case particularly with the undulating web mentioned above, the function of which during an impact depends on the construction of other parts of the bar (possible presence of ribs, intermediate walls, transverse walls etc).
The bar according to the invention could likewise have at least one of the following characteristics:
it has at least one zone in which, in cross section, the web has an average thickness less than average thicknesses of the front and rear walls;
the average thickness of the web is between 0.25 and 0.75 times the average thickness of each front and rear wall;
there are at least two zones, and said zones are each closer to the respective ends of the bar than to the middle of the bar;
in two zones each closer to the respective ends of the bar than to the middle of the bar, it comprises at least one rib perpendicular to the front and rear walls and to the web;
there are at least two ribs in each zone;
the ribs of each zone are connected to one another by reinforcing ribs, in particular ribs parallel to the front and rear walls;
in two zones each closer to the respective ends of the bar than to the middle of the bar, it comprises at least one cell extending between the front and rear walls;
the zones extend at right angles to a location for fixing the bar to longitudinal members;
it comprises at least one internal wall parallel to the front and rear walls;
there are at least two internal walls;
it comprises, in particular in a central zone of the bar, at least one intermediate wall at an angle to the front and rear walls and perpendicular to the web;
the intermediate wall forms a xe2x80x9cVxe2x80x9d when viewed from above;
the point of the xe2x80x9cVxe2x80x9d extends in the direction of the front wall;
the length of the central zone is at least equal to one third of the total length of the bar;
it is produced from plastic material reinforced by glass fibers; and
the fibers are unidirectional and continuous, at least in the front and rear walls;
According to the invention, a bumper bar for a vehicle comprising a bar according to the invention and a skin is also provided.
Other characteristics and advantages of the invention will become apparent from the following description of a preferred embodiment given by way of example, which is not intended to be restrictive.